AP BIOLOGY

Detailed explanation-1: -When a ligand binds to a cell-surface receptor, the receptor’s intracellular domain (part inside the cell) changes in some way. Generally, it takes on a new shape, which may make it active as an enzyme or let it bind other molecules. The change in the receptor sets off a series of signaling events.

Detailed explanation-2: -The ligand crosses the plasma membrane and binds to the receptor in the cytoplasm. The receptor then moves to the nucleus, where it binds DNA to regulate transcription.

Detailed explanation-3: -After the ligand binds to the cell-surface receptor, the activation of the receptor’s intracellular components sets off a chain of events that is called a signaling pathway or a signaling cascade. This process is sometimes called signal transduction.

Detailed explanation-4: -When a ligand binds to a protein, it undergoes a conformational change which in turn leads to a physiological response. The time a ligand spends attached to a receptor or specific protein is a function of the affinity between the ligand and the protein.

Detailed explanation-5: -Intracellular receptors require ligands that are membrane permeable and include receptors for steroid hormones, lipophilic vitamins, and small molecules such as nitric oxide and hydrogen peroxide.